Tab選項卡滑動，看算法就行

func selectLabelCenter() {
//計算選中label的centerX
        let centerX = CGFloat(self.segmentControl.selectedSegmentIndex)*itemWidth + itemWidth/2
//計算出應該偏移的offsetX
        var needScrollowOffsetX = centerX - slidingView.width/2
//最小值不能小於0
        if needScrollowOffsetX < 0{
            needScrollowOffsetX = 0
        }
//不能大於最大值(滑動至最右側)
        let maxScrollowOffsetX = slidingView.contentSize.width-slidingView.width
        if needScrollowOffsetX > maxScrollowOffsetX {
            needScrollowOffsetX = maxScrollowOffsetX
        }
//不需要滑動時不用滑動
        if needScrollowOffsetX != slidingView.contentOffset.x {
            slidingView.isUserInteractionEnabled = false
            UIView.animate(withDuration: 1.0, animations: {
                self.slidingView.contentOffset = CGPoint(x: needScrollowOffsetX, y: 0)
            }, completion: { (_) in
                self.slidingView.isUserInteractionEnabled = true
            })
        }
    }

出處